Device for sealing the place of penetration of a pipeline in the wall of a submerged structure

ABSTRACT

An axially flexible sealing device connecting two pipeline ends which comprises a number of sealingly connected annular members, each annular member including an inner cylindrical member, two spaced apart outer cylindrical members, and separate flexible ring members connecting the outer cylindrical members to the inner cylindrical member, each outer cylindrical member having a portion extending axially beyond the adjacent end of the inner cylindrical member when the attached flexible ring member is in an untensioned state. The sealing device is designed for use in connecting two pipelines located beneath sea level wherein the end of one of the pipelines is located in a hollow structure and one of the sealing devices is connected thereto, whereas the other end of the sealing device is sealingly connected to one end of a penetration sleeve which is sealingly connected through the wall of the structure (the other end of the sleeve being connected to the end of the other pipeline).

This is a division of prior application Ser. No. 941,731, filed on Sept.12, 1978, of Nick Noensie et al for "METHOD AND APPARATUS FOR SEALINGTHE PLACE OF PENETRATION OF A PIPELINE IN THE WALL OF A SUBMERGEDSTRUCTURE."

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a device for sealing theplace of penetration of a pipeline, especially in riser pipeline, in thewall of a submerged structure, which pipeline extends generallyhorizontally at the place of penetration and is connected to a generallyvertical section inside the structure, wherein an annular sealing devicewhich is flexible at least in the axial direction of the pipeline isplaced coaxially with the pipeline at the place of penetration, one endof the sealing device being connected tightly to the wall while itsother end is tightly connected to the pipeline.

2. Prior Art

One of the most desirable methods for transporting fluids like oil, gas,slurry, and water to and from offshore structures resting on the sea bedis through pipeline systems. The part of the pipeline system resting onthe sea bed is called a submarine pipeline, while the part which isconnected to the structure is called the riser.

The riser is vulnerable to many problems which range from corrosion andoverstressing to damage caused by supply vessels. Because of theseproblems the riser is subjected to thorough design considerations. Inorder to avoid wave loads and damage due to supply vessels, there hasbeen a tendency in resent years to place the riser inside the platformstructure. This necessitates the penetration of the pipeline through thewall of the platform structure. The area inside the platform structurewhere the riser is located can either be a wet or dry environment. Sincethe riser is located inside the platform structure and thus is in thevicinity of areas where people work, any damage to the riser can causeloss of human life. In order to maximize safety, the riser inside theplatform structure must be inspected periodically and minor damagerepaired to avoid catastrophic failure.

Underwater inspection and repair of the riser in a confined space insidethe platform structure are very hazardous operations. This space musttherefore be capable of being dewatered in order to allow inspectionand/or repair of the riser in a dry environment.

Therefore, whether the riser is in a dry or wet area, a safe sealingsystem must be provided at the place of penetration of the pipeline inthe wall of the pipeline structure in order to ensure maximum safetyduring repair, maintenance and inspection.

Theree are situations where large relative movement takes place betweenthe structure and the submarine pipeline. Such movements may be caused,for instance by, expansion of the pipeline due to temperature and/orpressure in the pipeline and movement of the structure due to externalinfluences like waves, current, wind and soil deformation.

Large relative movements between the pipeline and the platform structuremay thus give rise to high stresses and loads in the pipeline and inequipment and parts of the structure directly in the way of suchmovements, such as the seal and pipe support systems.

From U.S. Pat. No. 4,009,584 it is known to seal the place ofpenetration of a pipeline in the wall of a submerged structure, whereinthe pipeline by casting is fixed to the wall of the structure at theplace of penetration by means of epoxy or the like. The epoxy is said tobe sufficiently flexible to absorb minor relative motion between thepipeline and the structure, that is, minor movemens on in the order ofmagnitude of a few centimeters. One can assume however, that there mayoccur forces between the pipeline and the structure which are highenough to destroy the epoxy joint. In order to safeguard againstcatastrophic results of such an occurrence, a safety seal can bearranged around the joint, which seal generally has the form of astuffing box which is meant to prevent major leakage until the main sealcan be repaired. In one of the embodiments shown the safety seal isconnected to a bellow-like sleeve in order to give the safety seal acertain ability to move together with the pipeline without theoccurrence of sliding motion--and thereby leakage--between theseelements. However, the safety seal remains only a temporary emergencysolution until the main seal can be repaired. Such a pipeline beingrigidly held in or near the wall of the structure will readily besubjected to high loads at this place since it will serve as a fixedpoint when the pipeline seeks to move as a result of changes intemperature and/or pressure when the pipeline is put into service. Theseloads give rise to stresses which may be so high that danger of ruptureresults. Furthermore, such stresses can often lead to acceleratedcorrosion and cracking.

The object of the present invention is to provide a method and anapparatus of the type mentioned, whereby the above-mentioned drawbacksand deficiencies are generally avoided.

SUMMARY OF THE INVENTION

The method according to the invention thus permits the pipeline to moverelatively freely at the place of penetration when subjected totemperature and/or pressure changes when being put in service. Byletting both the sealing device and the vertical section of the riserpipeline be prestressed corresponding to the movement which is to beexpected when the pipeline is put in service, neither the seal nor thepipeline will be subjected to deflection stresses of any magnitude inuse, and the probability of a failure occurring in the critical areainside the platform structure will thereby be substantially reduced.

Since the sealing device may be built to any desirable length by puttingtogether a sufficient number of seal elements according to theinvention, the flexibility of the seal may be adapted to the expectedmovement of the pipeline at the place of penetration. The seal elementsare of a very robust and simple design and are very resistant both tomechanical and chemical influence. Furthermore, the sealing deviceaccording to the invention is easy to install and does not inviteincorrect assembly. Consequently, it satisfies generally all therequirements which may be imposed on such a sealing device.

For improved understanding of the invention, it will be described ingreater detail with reference to the exemplifying embodiments shown inthe drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a platform structure resting on the sea bedand being penetrated by a pipeline.

FIG. 2 shows, partly in section, an enlarged view of the place ofapplication of the invention at II of the structure in FIG. 1.

FIG. 3 shows, partially in section, a sealing device according to theinvention during installation.

FIGS. 4-7 show sections through seal elements according to the inventionin various load situations.

FIG. 8 shows partially in section a sealing device according to theinvention after installation, but before the pipeline is commissioned.

FIG. 9 shows the sealing device in FIG. 8 after commissioning of thepipeline.

FIG. 10 shows an alternative application in a platform having asupporting structure of steel.

FIG. 10a shows an enlarged view of the penetration point in the platformleg of the pipeline.

FIG. 11 shows an alternative examplifying embodiment of the invention,partially in section, used in close quarters.

FIGS. 12 and 13 show axial sections of some of the components of thesealing device in FIG. 11.

FIG. 14 shows the parts in FIGS. 12 and 13 installed together with afurther component of the sealing device.

FIGS. 15 and 16 show the sealing device in FIG. 14, partially insection, during two phases of installation of a pipeline.

FIG. 17 shows the sealing device in FIGS. 15 and 16 following completedpipeline installation.

FIG. 18 shows a further sealing device according to the inventionapplied for a pipeline having substantially smaller dimension than themaximum possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure 5 shown in FIGS. 1 and 2 is partially submerged in water2. The deck 15 of the structure 5 is situated in the atmosphere 4 abovethe water surface 3. The base 13 of the structure rests on the sea bed.The water depth 8 may vary; however, the present invention may be usedat water depths of 150 m or more.

As shown in FIG. 2, a submarine pipeline 6 is connected to the riserpipe 7 at point 19. The riser 7 penetrates the wall 12 of a passage 113in the base 13 of the structure 5 through a penetration sleeve 11. Aseal 10 keeps water 2 out of the areas 20 and 22 inside the structure 5,so that inspection and repair work may be performed as indicated in FIG.2 by means of a worker 21.

The riser 7 extends generally horizontally from the connection point 19outside the structure 5 to the area 22 inside a column 14 of thestructure. Here the riser extends generally vertically with a section 16up through the column to the deck 15 of the structure. The seal 10permits the riser 7 to move in the direction of the arrows 17 and 18while maintaining the sealing action.

FIG. 3 shows the seal 10 in greater detail. The seal consists of aplurality of individual seal elements 23 which are bolted together bymeans of flanges 24 into a row which forms the complete sealing device.One end 25 of the sealing device 10 is bolted to the penetration sleeve11, while the other end 26 is bolted to a flange 27 which is welded tothe riser pipe 7 to effect a permanent seal.

Each seal element 23 consists, as is apparent from FIG. 4, of an innercylinder 28 and two outer cylinders 29 of larger diameter and eachoverlapping an end of the inner cylinder 28, and two rings 31 ofelastomer material which is placed in between each of the overlappingparts 30 of the cylinders. The elastomer rings 31 are bonded to thewalls of the cylinders 28 and 29. The two elastomer rings 31 in eachseal element 23 can allow relative movement between the cyliners, assuggested in FIGS. 5, 6 and 7. FIG. 6 shows the inner cylinder 28 andthe outer cylinder 29 in unstressed condition without any displacementtherebetween. FIG. 5 shows the outer cylinders 29 displaced away fromeach other, while FIG. 7 shows the outer cylinders 29 displaced towardseach other.

The total relative displacement between the ends 25 and 26 of thesealing device 10 can be given any desirable magnitude by simplyadjusting the number of individual seal elements 23 to be boltedtogether.

The thick elastomer rings 31 connecting the inner cylinder and the outercyliners 29 will not easily be subjected to mechanical damage, and theywill therefore be able to resist quite a high differential pressure.Thus, the sealing device 10 will give a high degree of safety during itsentire lifetime.

The elastomer rings 31 may be made of synthetic rubber having a hardnessof 65 Shore A.

When the pipeline is in operation, the pressure and/or temperature ofthe fluid conveyed in the submarine pipeline 6 and the riser 7, 16during normal circumstances give a substantially permanent displacementof the riser 7, 16 and the seal 10 of magnitude 32 in the direction ofthe arrow 18 in FIGS. 2 and 9. In order to eliminate sustained stressesin the elastomer rings 31 and the riser 7, 16 due to this displacement18, the riser and the seal 10 is displaced or prestressed an equivalentdistance 32 in the opposite direction 17 before the pipeline sectionsare welded together.

This may be achieved, e.g., by means of a number of rods 33 attachedbetween the wall 12 and a point 35 on the riser 7. By tighteningturnbuckles 34 in the rods 33 the riser will be displaced acorresponding distance 32 in the direction of the arrow 17, andconcurrently the elastomer rings 31 will be compressed or prestressedthe same amount, as indicated in FIG. 8.

When the pipeline sections have been completely connected to each otherand the pipeline has been activated, i.e., a fluid is flowing throughthe pipeline system 6, 7, 16, the rods 33 are removed so that the riser7 and the seal 10 are allowed to move in the direction 18 a distance 32,as indicated in FIG. 9. This brings the elastomer rings 31 back to theirundeformed condition, and concurrently the bending stresses originatingin the vertical riser section 16 during prestressing of a seal, arereduced. The length of the horizonal section 7 of the riser between theseal 10 and the vertical section 16 is small enough that thermalexpansion of this section 7 will have insignificant effect on thestresses in the vertical section 16. According to the invention both theseal 10 and the riser 7, 16 during normal operating conditions aresubjected to the lowest possible loads. This is of major importance forthe safety and useful life of the installation.

The individual seal elements 23 may on one or more sides be equippedwith a coating for protection against corrosion and/or for givingelectrical isolation. Thus, the elements shown in FIGS. 3 and 4 areequipped with a rubber coating on the side facing inwards towards thepipeline.

FIG. 10 shows a sealing device 110 in accordance with the inventionapplied on a riser pipe 7 which extends into a leg 36 of a steelsupporting structure for a platform 37.

FIG. 11 shows a riser pipe, the horizontal section 7 of which extendsthrough the wall 36 of a hollow column of a steel structure. This riserpipe continues in a vertical section 16 inside the column. At the placeof penetration a penetration sleeve 11 is welded to the wall 36 of thecolumn. Between the penetration sleeve 11 and the riser pipe 7 isinstalled a sealing device according to the invention, here in a formrequiring little space inside the column.

The design of this sealing device will be apparent from FIGS. 12-14.FIG. 12 shows a flexible body consisting of two seal elements 23 whichare bolted together at adjacent flanges 24. The flexible body is placedon to a cylinder 38 which at one end is equipped with a flange 39. Theflange 39 is bolted together with the adjacent flange 24 of the flexiblebody. Thereafter the outer cylinder 40 is placed on to the flexible bodyand attached rigidly and tightly at one end to the flange 39, forinstance by welding. The other end of the outer cylinder 40 is equippedwith a flange 41. The flanges 24 of the flexible body are equipped withholes 42 in addition to the bolt holes, and in the one of these flangeswhich are attached to the flange 39, these holes have a somewhat smallerdiameter and are internally threaded for attachment of prestressingbolts 43 introduced through the larger holes in the other flanges 24.The prestressing bolts 43 are also equipped with threads at theiropposite, free ends, and nuts 44 are screwed onto these ends. Bytightening these nuts the flexible body will be compressed, as isapparent from FIG. 14. This figure further shows that the inner cylinder38, the flange 39 and the outer cylinder 40 together form a protectivehousing 45 for the flexible body.

In FIG. 15 the housing 45 is shown, together with the flexible body incompressed condition, installed in a penetration sleeve 11. The flange41 of the housing is attached to an inner flange 46 on the penetrationsleeve via a distance piece 47. The length of the distance piece 47 isadapted to the length of the housing 45 so that its annular bottom plate39 is located adjacent to a generally funnel-shaped guide 48 arranged atthe outside end of the penetration sleeve 11. The guide is preferablyformed so that the inner wall 38 of the housing forms an extensionthereof without stepwise transitions.

FIG. 15 also shows the end of a pipe 7 in the process of being pulledthrough the penetration sleeve 11 and the sealing device. The pipe endis equipped with a fixed ring 49, against which is resting a loose ring50. An elastic seal 51 is attached to the loose ring. During pulling inof the pipe end the seal 51 will be brought into contact with a rest 52fixed to the inwardly facing surface on the flexible body. A temporaryseal will hereby be formed, permitting water to be pumped out from theinside of the column in order for the sealing device according to theinvention to be attached permanently to the pipe. This is done byattaching a connecting piece 53 between the flexible body and the pipe,for instance by welding. As shown in FIG. 18, the connecting piece 153may preferably have a conical portion in order to reduce bendingstresses. After the connecting piece has been installed, theprestressing bolts 43 (FIG. 16) are removed, and the flexible body maynow follow movements of the riser pipe 7 with respect to the column wall36.

FIG. 17, and 18 show the condition of the flexible body when the riserpipe 7 has moved inwards the expected amount, for instance due tothermal expansion.

The sealing device according to the invention may easily be adapted topipelines having smaller diameter than the largest pipelines whichduring the design stage have to be expected and therefore will bedecisive for the diameter of the penetration sleeve 11. At this point itwill often not be possible to know the exact number and dimension of thepipelines that will have to be connected to the structure when it hasbeen placed on the sea floor. It is therefore necessary to providesufficiently many penetration sleeves with sufficiently large diameterin order to be able to cover the actual situation at a later stage.Should it become desirable to install a pipeline having substantiallysmaller diameter than expected, the penetration sleeve may easily beadapted to the new pipe dimension by means of the sealing deviceaccording to the invention. An example of such adaptation is shown inFIG. 18. The distance piece 47 is here given a smaller internal diameterthan the sleeve 11 so that a housing 45 for the flexible body adapted tothe particular pipe dimension easily may be attached. Furthermore, thefunnel-shaped guide 48 is equipped with an extension piece 54 which isformed so as to avoid a step transition between the guide and the innerwall of the housing. This is of importance for avoiding problems duringpulling in of the pipe and for avoiding unnecessary damage to the seal51. In order to further reduce the risk of such damage, the seal 51 mayalternatively be fixed to the rest 152 instead of sitting on the pipe 7.In FIG. 18 the rest 152 is shown to be arranged on the lower cylinder 28of the element 23. This positioning will usually be entirelysatisfactory, especially by smaller pipe dimensions. By larger pipedimensions, and especially when there is danger that the pipes may bepulled in somewhat misaligned with the axis of the penetration sleeve,it will usually be advantageous to arrange the rest 152 and possibly theseal 51 on the outer cylinder 29. Thus, the prestressing bolts 43 may beused to adjust the seating of the seal against the ring on the pipe andthis way stop any leakage due to insufficient alignment between thesecooperating parts.

We claim:
 1. A connecting system for sealing the penetration point atwhich a pipeline passes through a hole in a wall of a structure locatedbeneath the surface of a body of water, said hole including apenetration sleeve sealingly passing therethrough, and the pipelinehaving a fixed annular ring positioned therearound near the hole in thewall, said system including:a hollow outer cylindrical connection sleevewhich is extendable through the hole in said wall of said structure andwithin said penetration sleeve, one end of said outer connection sleeveincluding an outwardly extending flange means sealingly connected tosaid penetration sleeve and the other end including an inwardlyextending flange means, a hollow inner cylindrical sleeve positionedwithin said outer cylindrical sleeve, said inner cylindrical sleevebeing connected to said inwardly extending flange means of said outercylindrical connection sleeve, and an axially flexible sealing deviceconnected to said inwardly extending flange means of said outercylindrical sleeve and positioned to extend inbetween said outercylindrical sleeve and said inner cylindrical sleeve, said sealingdevice comprising at least one annular member, each annular memberincluding an axially extending inner cylindrical member, at least oneouter cylindrical member and a flexible ring member connecting each saidouter cylindrical member to said inner cylindrical member, each saidouter cylindrical member being positioned about said inner cylindricalmember such that with each said flexible ring member in an untensionedstate, each said outer cylindrical member will be separated from oneanother and will have a portion which extends in an axial directionbeyond the adjacent end of said inner cylindrical member, the outercylindrical member of said annular member located farthest from saidinwardly extending flange means of said outer cylindrical sleeveincluding an inwardly extending stop means for sealing abutment withsaid fixed annular ring of said pipeline.
 2. The connecting system ofclaim 1 wherein each annular member of said axially flexible sealingdevice includes two outer cylindrical members positioned about each saidinner cylindrical member, each said outer cylindrical member having aportion which extends in a axial direction beyond an opposite end of therespective inner cylindrical member when the flexible members whichconnect each outer cylindrical member to the respective innercylindrical member are in untensioned states, and wherein each of saidouter cylindrical members of each annular member include means forsealing attachment to one another and to, respectively, the pipeline endand said inwardly extending flange means of said outer cylindricalsleeve.
 3. The connecting system of claim 2 wherein a rubber coating islocated on the inside wall of each said inner cylindrical member of eachannular member, on the inside walls of each said outer cylindricalmembers on the portions thereof which extend axially beyond the adjacentends of said inner cylindrical member and on the portions of each saidflexible ring members which are exposed to the hollow cylindrical areadefined by said cylindrical members.
 4. The connecting system of claim 2wherein each said sealing attachment means for each outer cylindricalmember of each annular member comprises a flange with a hole meanstherein and connecting bolts passing therethrough to connect adjacentflanges together.
 5. The connecting system of claim 2 wherein saidaxially flexible sealing device comprises a multiplicity of annularmembers sealingly connected together.
 6. The connecting system of claim2 wherein said flexible ring members in each said annular member arecomposed of synthetic rubber having a hardness of about 65 Shore A. 7.The connecting system of claim 2 including means for compressing theaxial extension of said sealing device.
 8. The connecting system ofclaim 7 wherein said compressing means comprises a threaded elongatedbolt which is connectable to and extendable between said inwardlyextending flange means of said outer cylindrical sleeve and an outwardlyextending flange on the outer cylindrical member of said sealing devicelocated farthest from said inwardly extending flange means of said outercylindrical sleeve, and a nut means threadably engageable with saidelongated bolt to compress the outer cylindrical members of all saidannular members together.
 9. The connecting system of claim 2 whereinone end of the penetration sleeve includes a guide in the form of agenerally funnel-shaped inwardly-extending flange means.
 10. Theconnecting system of claim 9 wherein said penetration sleeve includes aflange means at the end thereof opposite said one end, and wherein agenerally U-shaped adaptor means is connected between said flange meansof said penetration sleeve and said outwardly-extending flange means ofsaid outer connection sleeve.
 11. The connecting system of claim 10wherein said generally U-shaped adaptor means has one leg longer thanthe other, the longer leg being connected to said flange means of saidpenetration sleeve, and wherein a funnel-shaped extension means isconnected to said funnel-shaped inwardly extending flange means of saidouter cylindrical member.
 12. The connecting system of claim 2 wherein aloose ring and an elastic seal means are positioned between saidinwardly extending stop means and said fixed annular ring on saidpipeline.